West Ham United Under-18s slipped to a slender 1-0 Barclays U18 Premier League defeat at Sunderland on Saturday, as Martin Smith's second-half penalty settled the contest.
The game's only goal arrived just after the hour, when Lynden Gooch turned smartly in the box, before being felled by Amos Nasha.
Smith took charge from the spot, slotting beyond Hammers keeper Sam Howes. It proved to be the winner, leaving manager Steve Potts to rue a string of missed chances.
He told whufc.com: "It's frustrating. We're left wondering how we failed to get anything from the game. We had a lot of the play, managed to create good chances and didn't take them. When it's like that, you never know, you're always vulnerable.
"The penalty gave them more of an incentive to hold on to a lead and we just couldn't break them down. But performance wise, there wasn't a lot wrong with it. It's just a case of whether we could put the ball in the back of the net and unfortunately we couldn't."
For Potts, defeat at the Academy of Light represented another missed opportunity for his young charges, after squandering a 3-1 advantage against Blackburn Rovers last time out.
"Last week, we were in a great position, played some really good stuff and then gave away a couple of sloppy goals," he continued.
"Minor mistakes cost us a win there and at Sunderland, our biggest mistake was not being ruthless enough in front of goal.
"We had very good chances to win the game and we didn't take them. The level we're at now, it boils down to what happens at either end. In between that, I thought we controlled the game. We were really good with the ball and I couldn't fault the boys in that regard."
West Ham United U18s: Howes, Knoyle, Page (Mavila 83), Nasha (Amoo 73), Burke, Harney, Makasi, Cullen, Brown, Bywater, Parfitt-Williams Subs not used: Bogard, Onariase, Girdlestone